It is known that the ring-opened polymers of bicyclo 2,2-1-heptene-2, generally called ring-opened polynorbornenes (hereinafter "polynorbornenes") and obtained by ring-opening polymerization of norbornene or its substituted derivatives, exhibit excellent compatibility with ester-type plasticizers such as dioctyl phthalate, dioctyl sebacate or butyl adipate and more particularly with the petroleum based or synthetic plasticizers of an aromatic, naphthenic and paraffinic nature. The preparation and properties of polynorbornene and its derivatives are for example described in French Pat. No. 1,535,460 of Jan. 12, 1967, corresponding to U.S. Pat. No. 3,557,072, and in French Pat. No. 1,536,305 of June 27, 1967, corresponding to U.S. Pat. No. 3,676,390, and its patent of addition French No. 94,571 of May 16, 1968, all of said patents as well as the French patent applications recited infra being incorporated by reference herein.
The rate of absorption of these plasticizers is particularly high with polynorbornenes in the form of a finely divided powder as obtained according to the process described in French Patent Application No. 74.10368 of Mar. 26, 1974, corresponding to U.S. Pat. No. 4,020,021. These finely divided polynorbornenes having a particle size of 0.01 to 2 mm, preferably of 0.01 to 0.8 mm, are able to absorb more than 7 times their weight of plasticizer of the aromatic or naphthenic type using simple mixing at ambient temperature.
It is generally known from French Patent Application No. 75.06213 of Feb. 27, 1975, corresponding to U.S. Pat. No. 4,137,210, that an appropriate choice of the amount and type of plasticizer makes it possible to obtain mixtures of polynorbornene and a plasticizer which maintain, after the constituents have been kept in contact for a sufficient period of time, a degree of fluidity which permits them to be simply poured, at ambient temperature, into molds, dies or other shaping means. Gelling then follows spontaneously and progressively at 1 to 24 hours after pouring. The finished article can then be removed from the mold or withdrawn from its shaping means. (See col. 1, line 46-col. 2, line 28, and col. 2, lines 34-49, of U.S. Pat. No. 4,137,210.) By way of example, one could mix, at ambient temperature, 100 parts by weight of polynorbornene having a particle size from 0.01 to 0.5 mm sold under the Trademark NORSOREX F by CdF-Chimie with 300 parts by weight of a petroleum-based or synthetic naphthenic plasticizer of medium or low density such as the oil sold under the Trademark SOMIL-B by Shell France, under the Trademark PIONIER SRW-8 by Hansen and Rosenthal, under the Trademark ENERTHENE 43 by British Petroleum and under the Trademark SUNTHENE 255 by Sunoil Co. The mixture obtained is ready for pouring into a mold 2 to 6 minutes after the constituents have been brought into contact and is completely gelled after 1 to 48 hours at ambient temperature.
The resultant gelled masses present numerous advantages. In particular, the rebound resilience can easily be varied over a fairly wide range. In practice, this varies as a function of the type and amount of plasticizer employed. Nevertheless, as these masses are not cross-linked, the residual set (permanent deformation) under mechanical stress, in particular under compression, is often too high. The residual set characteristics have already been improved by incorporating additives in the mixture, as described in French Patent Application No. 75.06213 of Feb. 27, 1975, of fillers and cross-linking agents such as sulphur, sulphur donors or peroxides so as to provide, within the body of the material, a three-dimensional cross-linked network. (See col. 2, line 50-col. 3, line 4, and the examples at col. 3, line 12-col. 4, line 21, of U.S. Pat. No. 4,137,210.) The fillers and cross-linking agents are generally incorporated by dispersing them into the plasticizer at a rate of 1 to 10 parts by weight to 100 parts of polynorbornene before adding the plasticizer to the polynorbornene.